1. Field of the Invention
The present invention relates to a gas turbine and a method of cooling the high temperature section of gas turbine.
2. Description of Prior Arts
To meet growing demands for electric power in recent years and to combat global warming, it is necessary to increase the capacity and enhance efficiency of gas turbine power generation facilities. Especially in gas turbine power generation facilities where fuels are supplied and burnt with air compressed by a compressor and fed to the combustor and the gas turbine is driven by this combustion gas, large capacity and high efficiency can be achieved by further increasing fuel temperature. In this case, however, the gas turbine for collecting energy of the combustion gas exposed to high temperature will be damaged and a serious accident may occur if it is not cooled. So in gas turbine power generation facilities where combustion gas temperature is high, compressed air and steam are used to cool the high temperature section of gas turbines.
With consideration given to possible pressure loss in the flow path of cooling air, high-pressure air is used as cooling air for cooling the high temperature section of a turbine.
In an open cooling gas turbine where cooling air is discharged into the turbine gas path, air extracted from the low-temperature compressor is directly used as cooling air. Air discharged from the compressor is cooled by a cooler, and is used to cool high temperature sections.
In a closed cooling type gas turbine where cooling air used to cool the high temperature section of the turbine is collected into the combustor and is used as combustion air, there is pressure loss of cooling air in the flow path of the turbine high temperature section. So in order to collect cooling air into the combustor, the pressure of air discharged from the compressor must be increased by a boost compressor. If it is increased by the boost compressor, cooling air temperature will rise. This requires installation of a cooler which adjusts the cooling air temperature to an appropriate level.
For example, JP A No. 10-196316 discloses a system configuration where air discharged from the compressor is cooled by a heater exchanger to cool the high temperature section of a turbine.
When the turbine is started, the temperature of coolant used by a heater exchanger for cooling the cooling air is low, and cooling air temperature at the heater exchanger outlet is reduced excessively, with the result that mist may occur in the cooling air downstream from the heater exchanger. If mist occurs in cooling air, dust contained in cooling air may be deposited on the wall surface of the cooling flow path. Further, if multiple dust particles are combined to big lumps of dust, a complicated and elaborately formed cooling flow path formed on the turbine high temperature section may be locked. Further, the auxiliary machines constituting the cooling air system may be damaged. Especially the boost compressor constituting the system is a rotary body driven at a high speed. So if mist in air with high-speed air flow is supplied to the boost compressor, it will collide with the impeller at a high speed, with the result that the compressor may be damaged. If the boost compressor is damaged, supply of cooling air to the turbine high temperature section may be suspended, and the turbine high temperature section cooling flow path may be closed due to intrusion of foreign substances. This may cause damages.
Furthermore, deposition of mist on the equipment forming the cooling air system may cause rust inside the equipment. Such rust will turn into dust generated newly in the cooling air system, and will become a new factor to block the cooling air flow path. For these reasons, if such an event occurs to the cooling air system, cooling air cannot be maintained clean even if the equipment constituting the cooling air system is provided with a high-performance filter capable of separating fine dust is provided. Such a cooling air system is not suitable for cooling the high temperature section of the turbine.
The object of the present invention is to avoid occurrence of mist in the cooling air system of the gas turbine.
A gas turbine according to the present invention comprising a compressor for compressing air, a combustor for mixing air compressed by the compressor with fuel and burning them, and a turbine to be driven by combustion gas burned by the combustor is characterized by further comprising;
a cooling air system for supplying part of air compressed by said compressor to the high temperature section of the turbine;
a heater exchanger for exchanging heat of part of air compressed by the compressor, this exchanger installed on the cooling air system; and
a system for adjusting air temperature on the downstream side of the heater exchanger in conformity to the operation time of the turbine.